Abstract Class In C++ (Interfaces)

In C++, abstract classes are used to accomplish abstraction. Abstraction is the process of hiding internal details and displaying only functionality in C++. There are two approaches to create abstraction:

1. Interfaces
2. Abstract Class

Both the abstract class and the interface can have abstract methods, which are required for abstraction.

Abstract Class:

In C++, a class is abstracted by declaring at least one of its functions to be pure virtual. In the declaration of a pure virtual function, the keyword “= 0” is used. Derived classes must provide the implementation.

Let’s look at an abstract class in C++ that has only one abstract method: draw (). Rectangle and Circle are two derived classes that implement it. Both classes are implemented differently.

#include <iostream>  
using namespace std;  
class Shape    
{    
    public:   
    virtual void draw()=0;    
};    
 class Rectangle : Shape    
{    
    public:  
     void draw()    
    {    
        cout < <"drawing rectangle..." < <endl;    
    }    
};    
class Square : Shape    
{    
    public:  
     void draw()    
    {    
        cout <<"drawing square..." < <endl;    
    }    
};    
int main( ) 
{  
    Rectangle rec;  
    Square cir;  
    rec.draw();    
    cir.draw();   
    return 0;  
}

Output:

drawing rectangle...
drawing square...